Hello all,
I'm hoping someone can point me in the right direction here as I've been racking my head trying to find a solution to my problem.

I would like to include a masthead image in my tumblr theme however I do not know how to properly go about doing so.
This is my current theme: Theme
I want to include a masthead image with title and description like in this image: Reference
I would like to keep the sidebar, avatar, and menu links where they are in the left side. The only thing I want to add is the image up top with the title and description. I'm hoping someone can help me figure this out.

I've included a file with the HTML code for my current theme.